Ethernet switching devices, such as switches, routers and the like, maintain the information required to directly forward Ethernet messages to the proper port on that switch for only a limited amount of time, such as three minutes. Ethernet switching devices may include devices whose primary purpose is to operate as Ethernet switches, as well as devices that have a different primary purpose, but can also perform some or all of the conventional Ethernet switching functions.
The information used to send a message from device A to device B is identified from messages that previously traveled in the other direction, that is, using messages that were sent from device B to device A. If the switching device does not know how to forward the message, the message will be sent to many virtual or physical connections supported by that switch until the proper path is determined in either direction. Virtual connections are supported by logical ports and there may be more than one logical port supported by a physical port. Because each physical port may support multiple logical ports, and because the switching device will send the message to each logical port, when logical ports share the same physical port, this process takes even more of the bandwidth for each physical port and on the network. This flooding of traffic can significantly multiply the traffic impact of a message on the network. (The use herein of the term flooding is different from the strict definition of flooding, in which traffic is generated to every port, physical or logical, other than the port from which the message was received. Ethernet flooding is somewhat more intelligent and so the message may not go out over every port, but may go out over many ports or more than one port).
The more switches there are between the destination and a switching device, the less likely that switching device will have recently received a communication from that destination device, and therefore that switching device will not know how to route messages to that device as a destination. When other switching devices that do not know how to route the message receive the message, they will flood the message to other active logical ports on the switch (except the port on which the message originated and other ports in the direction of the source), causing the message to be received by many devices on the network that are not on the best path from the source of the message to its destination. In a full mesh network, in which each switching device is coupled to every other switching device, such flooded messages can traverse a significant portion of the network. The devices will also receive the message before determining that the message is not for them, impacting the available network bandwidth for that device and, if charges are assessed for bandwidth used, raising the costs borne by each device for receiving traffic that they do not wish to receive. Thus, not only is there an adverse effect on the network traffic, there can also be an adverse effect on every device in the network. In a network in which customers pay for traffic, it can be a significant added expense when traffic is flooded in this manner.
Sometimes, none of the switches will have any forwarding information for a device even if several messages are sent to that device. For example, if messages are sent in only one direction, from device A to device B, but no messages are sent in the reverse direction, each message may be flooded by a number of switching devices in the path from A to B, because they will never have received a message from device B. Thus, the flooding problems can recur in message after message.
In a conventional wide area Ethernet network, routers may generate a significant amount of traffic over the Ethernet network of switching devices. If the routers send conventional messages to one another, the first such message (typically an ARP message, but other types of messages may be used as an initial message) will be flooded, but subsequent messages (typically routing messages, such as BGP messages or OSPF messages, but again other types of messages may be sent) will be sent using a single path, if the routers are set up to send the subsequent messages more frequently than the Ethernet switching devices discard the paths. When the routers send other communications to one another, again the messages will not be flooded by the Ethernet switching devices because such messages will cause the switching devices to always retain the proper port identifier to use to send a message from one router to another. Thus, only the first such message is flooded. Because the initial message is short, typically 64 bytes, the flooding of such a router to router message does not generate large amounts of traffic and is considered an ordinary part of the traffic in an Ethernet network.
When routers communicate using conventional methods, the routers arrange point to point communications to each of the other routers with which that router will communicate. As the number of routers grows, the point to point communications can cause too much overhead to be maintained, and so another solution may be used for subsequent messages, such as BGP messages or OSPF messages. This other solution uses one or more route servers to communicate with each of the routers in the network. BGP or OSPF messages are sent only to the route server by each of the routers and the route server distributes them to the other routers, keeping the overhead on each router low. However, because the keepalive messages from any router are shunted to a route server, other switching devicees will not receive the BGP messages from each router, and thus the return path to a router will not be known by any switching device not in the path between a router and the route server it uses when it is time for one of the routers behind any such switching device to send messages to that router.
Thus, many many messages will be flooded, and those messages may be significantly larger than 64 bits. The impact on the network, and the impact on traffic paid for by the customer, can thus be significant when a carrier migrates to route servers.
It can be difficult to manually maintain information about a network, because devices can be disconnected from the network and reconnected for various reasons. It can be desirable for any solution to the above problem to be automatic, so that information about devices coupled to the network does not have to be manually entered and changed.
What is needed is a system and method that can reduce the need to flood messages in a network such as an Ethernet network when route servers are used that is managed in an automated fashion.